Why did Allah specifically mention the age of forty in the Quran, and does this mean that young people have more leeway in their religion?

The age of forty is the age of attaining the perfection of intellect and understanding, and the peak of the culmination of Allah's blessings upon a human being. It is a stage subsequent to reaching full maturity, as stated in His Almighty saying: (Until, when he attains his full maturity and reaches [the age of] forty years, he says, "My Lord, enable me to be grateful for Your favor"). Al-Qurtubi mentioned that whoever reaches forty years of age should realize the extent of Allah's blessings and be grateful for them, and that some scholars isolated themselves from people upon reaching this age. Ibn Kathir clarified that the intellect is perfected and understanding and forbearance reach their peak at this age, and it contains guidance for renewing repentance and turning back to Allah. Al-Shawkani added that full maturity (ashudduhu) may be reaching puberty, and that reaching forty is something beyond that, and that prophets were not sent until after forty. The age of forty is not a limit for accountability and punishment, as puberty is the criterion for religious obligation (taklif). However, what is intended in the verse is that this age marks the complete maturation of intellectual and physical faculties, which motivates one to give thanks for Allah's blessings and to dedicate one's life to His obedience.